1. Technical Field
The present invention relates to a device and a method for deflecting a laser beam. The present invention relates, in particular, to a device and a method for deflecting a laser beam with a deflection mirror arranged displaceably about a rotation axis.
2. Related Art
For the purpose of scanning an image region or a working region in the course of material processing, light beams (laser beams) are deflected in one or two scanning directions (x/y scanning direction) by means of suitable deflection devices (scanners). Preferably, in order to avoid vignetting, in this case approximately collimated light beams are pivoted about the centre of the entrance pupil of a focusing optical unit. The deflection of the light beams is generally performed with pivotable mirrors, for example with galvano scanners, piezo scanners, polygon scanners or resonance scanners.
WO2006074898 describes a laser treatment apparatus which images a laser beam with the aid of two mirrors mounted on galvano scanners, and with intermediate imagings through a relay optical unit in each case, into the entrance pupil of an objective.
EP1584310 describes a system having two scanning axes with only one relay optical unit, but in return with an additional synchronously moved mirror for the second scanning axis, which mirror prevents the beam deflected by the second scanning axis from impinging on the first rotation axis outside its centre of rotation.
EP 1 557 710 describes an optical scanner for imaging apparatuses such as a printer, copier or fax machine, in which the light beam impinges obliquely on a deflection mirror during the imaging process, said deflection mirror being embodied such that it is narrower in the direction of the rotation axis. In accordance with EP 1 557 710, the light beam is projected onto the deflection mirror with a beam width that is reduced but surpasses the mirror width (“overfilled” scanner). In order to counteract an imaging of the deflected light beam that is rotated depending on the deflection angle of the mirror (by axial rotation), the deflected light beam is thereby trimmed depending on the rotation angle.
U.S. Pat. No. 6,341,030 describes a further “overfilled” scanner for imaging apparatuses, in which the light beam impinges obliquely on deflection mirrors embodied as facets of a rotating polygon mirror, the light beam width reduced by optical beam-shaping means surpassing the mirror width of the individual facets in the scanning direction.
In order to produce high scanning speeds, mirrors with the lowest possible inertia (that is to say, in particular, small mirrors) are desirable. In this case, on account of fundamental optical laws for given imaging parameters of the focusing optical unit (focus size, working distance and image field height), the mirror size cannot be reduced without thereby simultaneously increasing the scanning angle. Conversely, the beam diameter has to be increased for a likewise speed-increasing smaller scanning angle. Formally, the product of beam diameter and scanning angle is a constant of the optical system. The simultaneous reduction of the mirror diameter and of the scanning angle desired for the purposes of increasing the speed fundamentally cannot be realized.